PHOENIX (AP) - The Arizona Diamondbacks were hurt by another rough outing by a starter. They were unable to get the big hits when they needed them.

Some stellar defense by San Diego certainly didn't help.

The Diamondbacks are in a rut, one that's left them scratching their heads.

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Trevor Cahill struggled in the first inning again and Arizona failed to build momentum after Aaron Hill's two-run homer in the eighth inning, sending the Diamondbacks to a 5-4 loss to the Padres on Sunday.

Arizona has lost three straight and five of seven. It dropped to 4-10 in its last 14 home games.

``When you get into streaks like this, sometimes it doesn't seem fair,' Arizona manager Kirk Gibson said. ``There (is) no rhyme or reason, but it is the way it worked out for us.'

Everything seems to be going right for San Diego.

The Padres came into the game on a roll, winning the series' first two games by a combined score of 14-3 for their second six-game winning streak in August.

They kept it going with the same formula: good starting pitching, superb defense and a bunch of hits.

San Diego roughed up Cahill (9-11) and had at least 10 hits for the sixth time in eight games. Padres starter Edinson Volquez (9-9) recovered after a shaky first inning and San Diego's bullpen escaped some sketchy moments of its own. The defense, particularly up the middle, was stellar all day, no matter who was pitching.

Altogether, it lifted the Padres to their second sweep in the desert this season and sixth straight win over Arizona, matching a franchise record against the Diamondbacks.

``We're playing pretty good right now,' Volquez said.

The Diamondbacks are not.

After collecting two runs and three hits in the first inning, Arizona had one more hit off Volquez over the next six innings. Hill connected against Brad Brach in the eighth to pull Arizona within one, but Padres shortstop Everth Cabrera made a spectacular diving stop at the edge of the grass on a grounder by Justin Upton.

The Diamondbacks still had a chance, but Luke Gregerson escaped a jam to finish off the eighth, then pitched a perfect ninth for his first save since 2010.

Arizona made a big run to the NL West title last season, but it's running out of time to do it again.

``As a clubhouse, we still believe in ourselves right now,' center fielder Chris Young said. ``It was a tough series, but at the same time it is still not over yet. We will continue fighting and play better baseball and see where we end up.'

Cahill has been plagued by slow starts and Sunday was no different.

Moved up in the rotation after Arizona traded left-hander Joe Saunders to Baltimore, Cahill opened with a couple of groundouts before giving up a single to Chase Headley. The right-hander then walked Carlos Quentin to set up Yasmani Grandal's run-scoring single and Yonder Alonso made it 2-0 with another single.

Cahill drew a few boos from the home crowd after walking Mark Kotsay to load the bases before ending the threat with a groundout. He needed 32 pitches to get through the first inning and has allowed 19 runs in the opening frame in 26 starts.

Cahill had more two-out problems in the third inning, giving up a run-scoring single to Kotsay after hitting Grandal with a pitch and Alonso's single. He allowed another run in the fourth on a single by Quentin that made it 4-2 and was done after walking Grandal to load the bases with two out in the inning.

The Padres had eight of their 11 hits off Cahill, who allowed at least four runs for the third time in four starts.

``I didn't throw the ball real well,' Cahill said. ``When I made good pitches, they still found holes and that makes it tough.'

Volquez had similar first-inning problems, giving up two-out RBI singles to Miguel Montero and Young.

The right-hander settled into a groove after that. He allowed two runs and four hits for his second straight quality start after allowing at least four runs in four straight outings.

The Padres gave Volquez plenty of help, too.

Second baseman Alexi Amarista made several spectacular stops, the best of the bunch coming in the second inning, when he ranged behind the bag and made a jump throw to get Jake Elmore by a half-step at first.

Cabrera topped him in the eighth inning, with a how-did-he-do-that stop to get Upton at first and squelch Arizona's momentum.

``That's one of the best plays I've seen,' Padres manager Bud Black said. ``An unbelievable play.'

Gregerson later struck out Chris Johnson with runners on second and third in the eighth while extending his scoreless streak to 22 games. He also made a diving stop to get pinch-hitter Jason Kubel for the second out in the ninth, and San Diego went on to its seventh straight win at Chase Field.

NOTES: A three-man umpire crew officiated the game after crew chief Tim Tschida, who was slated to work third base, was scratched due to ``personal medical reasons.' ... Upton extended his home hitting streak to 19 games with a single in the first inning. ... Arizona LHP Tyler Skaggs, Monday's starter against Cincinnati, earned the win in his major league debut on Wednesday after allowing two runs in 6 2-3 innings against Miami. ... RHP Casey Kelly will make his major league debut for the Padres on Monday night against Atlanta. He was part of the 2010 trade that sent first baseman Adrian Gonzalez to Boston.